Letters

zil, , Indonesia, and Zimbabwe, are receiving sub- egy to make the technology available and affordable. stantial support from bilateral and multilateral develop- ment sources. The success of these initiatives should References : Annan, R., Malbranche, P., Hurry, S., 1992, ‘‘Strategy for disseminating/commercial- further open the door to international financing for solar- ising proven renewable energy technologies’’, Prospects for Photovoltaics -- Com- based rural electrification and thus help to remove a criti- mercialization, Mass Production and Application Development, Advanced Technology cal barrier to the widespread use of solar electric Assessment System, Issue 8, United Nations Department of Economic and Social Development, pp. 153-159. technology in rural areas. Empresa Electrica de Guatemala, 1993, ‘‘Proyecto Piloto Fotovoltaico’’, LUCES #31, pp. 10-11. 6. Conclusion Inversin, A., Mettler, R., Hansen, R., Freymiller, F., Berkowitz, D., 1991, ‘‘Technical and financial assessment of electricity supply options for rural villages in southern Solar-electric systems have proven reliable and cost-ef- Belize’’, National Rural Electric Cooperative Association, Washington, D.C., USA. fective in the Dominican Republic, where thousands of Van der Plas, R., de Graaff, A., 1988, ‘‘A comparison of lamps for domestic lighting people are now enjoying the benefits of electricity for the in developing countries’’, Industry and Energy Department working paper, Energy Series paper #6, World Bank Industry and Energy Department, PPR, Washington, first time. The program’s success can be largely attributed D.C., USA. to the strength of local participation and a targeted strat-

tilised supply of agro-processing residues: around 49 mil- Development of an lion tonnes per annum (National Productivity Council, appropriate 1987). For a number of reasons, mainly social and envi- ronmental, it is not practical to consider using crop resi- briquetting technology dues, such as rice straw, as a (Clancy, 1991). A major disadvantage of agricultural residues as a fuel suitable for production and is their low bulk density, which makes handling difficult, use in developing countries transport and storage expensive, and gives rise to poor properties. However, these problems can be overcome by compacting, with a compression ratio of ap- P.D. Grover and S.K. Mishra proximately 7:1, the loose biomass to form . The Biomass Conversion Laboratory, Dept of Chemical opportunity to utilise more efficiently agricultural resi- Engineering, Indian Institute of Technology, dues, with a reduction in levels, has in recent New Delhi-110016, India years aroused the interest of developing countries, as well J.S. Clancy as some industrialised ones, in briquetting. Briquetting is a relatively new technology for develop- Technology and Development Group, University of Twente, ing countries. Although there are a number of different PO Box 217, 7500 AE Enschede, The Netherlands. briquetting technologies commercially available, the chal- lenge is to find a technology which is suited to the local 1. Introduction market, both in terms of the briquetting press itself for Biomass energy currently plays a major role in meeting local manufacture and the briquettes. In this short com- the present energy needs of developing countries. A num- munication we wish to report on our initial experimental ber of authors (see for example, Beyea et al., 1991), have results in trying to develop an appropriate briquetting also expressed the view that biomass has the potential to technology which meets both the technical and socio-eco- meet the additional energy demands of urban and indus- nomic criteria to be a sustainable technology, as well as trial sectors, thereby making a significant contribution to bringing environmental benefits. the economic advancement of developing countries. If this Although there are many briquetting plants installed by new role is to be achieved within the context of sustain- entrepreneurs in India, which have mainly used the piston able development, it is important for a extrusion presses, they have not been a complete success such as India to achieve both sustainable biomass fuel because of the variation in raw materials and a number production and the more efficient utilisation of biomass. of socio-economic constraints. The technologies used However, in order for biomass to make a significant im- have also been expensive and unreliable. They generally pact as a fuel there is a need to improve and promote require high maintenance and use excessive amounts of state-of-the-art technologies. power. Sometimes the briquettes have been found difficult Of the various renewable energy sources, bio-residues, to ignite or burn slowly, with high levels of smoke. Also, of which agricultural residues form a major component, because of irregular production patterns, arising from the can be most easily utilised to reduce the consumption of intermittent breakdowns of the briquetting machines, the woodfuel (blamed partly in some areas as a factor in de- briquettes have not been able to penetrate the fuel market forestation) (Hosier and Svenningson, 1987). Since most in the industrial sector. However, the potential does exist, developing countries’ economies are still primarily agri- due to the problems of intermittent solid fuel supplies in culturally based, they produce huge quantities of agricul- India, for a correctly designed and engineered process to tural residues which provides an enormous untapped fuel allow a reasonably attractive energy recovery from bio- resource. For example, in India there is a large, underu- residues. The plant capital for the operation should be

Energy for Sustainable Development l Volume 1 No. 1 l May 1994 45 Letters

modest and the value of the fuel attractive for the indus- briquetting technology. The R&D strategy has been to re- trial market. Therefore, a briquetting technology finan- duce both the wear of the screw due to friction and the cially viable and convenient to use would ensure adoption high power consumption. Any savings in power consump- of the technology by local entrepreneurs and the bri- tion can then be utilized to increase the throughput ca- quettes by the industrial sector. pacity of the machine (Bhattacharya et al., 1985). 2. Present status of briquetting technologies 3. The screw press technology In India, the briquetting industry started in 1981 with the The press being used as part of the test work reported introduction of low density and high density technologies. here is the Shimada SPMM-850 KS, which has a screw The former technology requires of the biomass which rotates at a speed of 600 rpm and this compresses followed by briquetting using a binder, to maintain the the material against a heated die. The die is heated to a structure. On the other hand, high density briquetting temperature of 280 to 290oC to give a smooth extrusion technology compacts the biomass and holds the structure of the briquettes. The production capacity of the machine together without a binder. These briquettes are more ac- depends on the size. At present briquettes of 55 ceptable to the industrial user. mm diameter are produced with a capacity of 400 kg/hr. There are two basic types of high compaction technol- If a 65 mm diameter die is used then the capacity in- ogy: the piston press and the screw press. Most of the creases to 650 kg/hr. This factor is quite important in the units presently installed in India are of the reciprocating financial analysis of the whole plant and in the calculation piston type, where the biomass is extruded through a die of the manufacturing cost of the briquettes, and hence by a reciprocating ram at a very high pressure. In a screw selling price. extruder press, the biomass is extruded continuously by a screw through a heated taper die. In a piston press, the Table 1: Comparison between screw extruder and piston press wear of the contact parts, for example, the ram and dies, is less compared to the wear of the screw and dies in a Piston press Screw extruder screw extruder press. The power consumption in the for- Optimum moisture con- 10-15% 8-9% mer is less than that of the latter. However, in terms of tent of raw material briquette quality and production procedure the screw Wear of contact parts low in case of high in case of press is superior. The central hole in the briquettes pro- ram and die screw duced by a screw extruder helps in uniform and efficient combustion, with significant reductions in smoke. Also Output from the ma- in strokes continuous chine these briquettes can be carbonised which increases their energy density. The briquettes are stronger than from a Power consumption 50 kWh/tonne 60 kWh/tonne piston press, making them less prone to breakage which 3 3 Density of briquette 1-1.2 gm/cm 1-1.4 gm/cm reduces losses during handling and in the furnace. Table 1 shows a comparison between screw and piston presses. Maintenance high low The screw extruder press looks to be the most promis- Combustion perform- inclined to burns well with ing technology, with its advantages outweighing its dis- ance of briquettes crumble on grate, minimal smoke advantages. Also there has been a high degree of success smoky with machines in Europe and Japan. However, a screw Carbonisation to char- not possible possible extruder machine most suited to the most appropriate bri- quette production rate in rural India (below 1 tonne/hr), which is linked to the levels of raw material availability, Suitability in gasifiers not suitable suitable is not manufactured in the country. Local manufacture of Homogeneity of non-homogeneous homogeneous the press is an important factor in guaranteeing the sus- briquettes tainability of the technology, by ensuring that the skills for maintenance and after-sales service are indigenous and hence readily available. A criticism levelled at imported technology is that real technology transfer does not take place which rapidly leads to equipment being either aban- doned or operated inefficiently. In an attempt to overcome these problems and provide a technology which is suited to local manufacture and adapted to local feedstocks, a collaborative project has been under way for the last year between the Indian Institute of Technology, Delhi, the Technology and Development Group, University of Twente, The Netherlands and Densitec BV (a private com- pany also based in the Netherlands). This project is in- tended to overcome the technical and economic difficulties which will help in a wider dissemination of Fig. 1. Layout of a briquetting plant with preheater

46 Energy for Sustainable Development l Volume 1 No. 1 l May 1994 Letters

The screw press has initially been tested with . Research Institute (TERI) is carrying out a financial The moisture content of the sawdust available in India analysis of briquetting technology and assessing the mar- usually varies from 25 to 30%. Drying the material re- ket for briquettes to help design a better strategy for the duces the moisture content to an optimum amount of 8 wider dissemination of both the technology and briquettes to 9% and sieving allows material of suitable particle size as a fuel. Initial results have shown that a general finan- (<6 mm) into the press. cial analysis is difficult since results are very site-specific. This problem is compounded in India, due to the size of 4. Test programme and results the country giving such diverse geographical areas and The whole briquette plant has been operated initially with- different operating climates which lead to wide variations out a pre-heater to give baseline performance data. in raw material prices and transport costs. During the briquetting process the abrasive wear on the The key factors for the consumer are the price of the screw is extensive. At a certain point when the surface briquettes and their relative performance compared to metal loss is unacceptable the screw no longer functions other available . Briquettes can be a major competitor and must be replaced. This time interval is known as the to, and readily substitute for, coal, wood or lignite. It standing time and has a significant effect on the briquette would appear that Rs. 1,200 to 1,400 ($1 = Rs. 30 ap- price since changing the screw interrupts production. The prox.) per tonne is the acceptable cost at present. This more often the screw is replaced the more frequently pro- sets the target for the development of the technology to duction is disrupted. reduce costs to a By applying a suit- level which will al- able hard facing al- low briquettes to loy, the standing penetrate the fuel time of the screw market in India. can be improved. A The cost of the number of different briquette depends hard facing alloys almost entirely on readily available in the life of the screw India have been instead of other tested as part of this costs such as labour, work. The best re- energy (used to op- sults have been erate the machine) found with tungsten and transport. This carbide, which is confirms the impor- also the cheapest tance of increasing hard facing alloy in the life of the screw India. The standing A general picture of the plant to decrease the cost time has been in- of the briquettes. creased from four to 15 hours without pre-heating the ma- Table 2 shows some of the other major shortcomings terial. of briquetting technology that have been identified as part The standing time can be further augmented by pre- of this study. These problems also have to be addressed heating the raw material. Pre-heating improves the per- if there is to be widespread acceptance of the process. formance by softening the biomass and reducing the load on the screw. In the second phase of the test programme, Table 2: Major shortcomings hindering the wider dissemination of a thermic fluid pre-heater has been installed, to raise the briquetting technology material temperature to 120 to 140oC in order to study Financial Selection of raw materials the effect on the power consumption and standing time Site specific of the screw against wear. Reductions in power consump- Seasonal (eg operation not possible during tion between 30 and 40% have been found. Also the pick- monsoon) up characteristic of the material improves, giving a smoother output. Technical Production rate Maintenance procedures The feed temperature is not critical for the production Wear cost of good quality briquettes. Expertise Emphasis in the test programme continues on improv- ing the life of the screw. This will be followed by opti- Users’ acceptance Related fuel market misation of the briquetting process and obtaining Demand patterns performance data on other potential feedstocks, such as Environmental Dust/smoke emissions bagasse pith and coffee husk. Competition with wood 5. Implementation strategy 6. Conclusions A definite potential and demand for the briquetting tech- In a parallel component of the project, the Tata Energy

Energy for Sustainable Development ! Volume 1 No. 1 ! May 1994 47 Letters

lifetime has been shown to be the key factor in reducing briquette production costs. Research, the initial results of which are reported here, to improve screw lifetime and the other main problem with the screw extruder, its high power consumption, are showing promising progress in achieving these aims. Results have shown that application of a suitable hard facing alloy to the surface of the screw increases the standing time significantly which has im- portant implications for costs and continuity of produc- tion. Pre-heating the biomass has been shown to reduce power consumption between 30 and 40%. A view of the screw press and the product obtained from the plant nology and briquettes has been confirmed in India. Bri- quettes could penetrate the commercial fuel market in the References Beyea, J., Cook, J., Hall, D., Socolow, R. and Williams, R. (1991), ‘‘Towards Eco- short term with an appropriate marketing strategy. How- logical Guidelines for Large-Scale Biomass Energy Development.’’ Report of a Work- ever, a number of problems of technical, social, environ- shop for Engineers, Ecologists, and Policy-Makers convened by the National Audubon mental and economic nature have also been recognised Society and Princeton University. Bhattacharya, S.C., Bhatia, R., Islam, M.N. and Shah, N. (1985), ‘‘Densified biomass which need to be addressed to achieve a wider dissemi- in Thailand: Potential, Status and Problems.’’ Biomass, 8, pp. 255-266. nation of a more sustainable technology. Clancy, J.S. (1991), ‘‘Agricultural Residues in India: Their Potential as Briquetting The price of briquettes and their fuel quality compared Feedstock.’’ Working Paper No. 52, Technology and Development Group, University of Twente, The Netherlands. ISSN: 0923-8700. to other fuels have been determined as the most signifi- Hosier, R. and Svenningson, P.J. (1987), ‘‘Biomass briquettes in the Dominican Re- cant parameters for the consumer. public Part I: Social and Economic Feasibility.’’ Biomass, 13, pp. 199-217. Screw extrusion has been identified as the most appro- National Productivity Council (1987), ‘‘Improvement of Agricultural Residues and Agro-Industrial By-Products Utilisation.’’ All-India Report prepared for DNES, Ministry priate technology for the developing countries. The screw of Energy, New Delhi, India.

production because the dairy cattle are zero-grazed. The An integrated biogas/fodder 4 ha plots are all subdivisions of one large tract of land. project for small scale dairy The households on adjacent plots are anything from about farmers in Rusitu, Zimbabwe M.C. Mapako Biomass Users’ Network Africa Regional Office Post Bag 7768 Causeway, Harare, Zimbabwe

The Biomass Users’ Network (BUN) is a South-led inter- national non-governmental organisation with offices in Sao Paulo, Brazil (Head Office), Costa Rica, Thailand, and Zimbabwe (regional offices), a liaison office in Wash- ington as well as an information and skills office in Lon- don. The Africa Regional Office in Harare, Zimbabwe is in- volved in numerous biomass related projects. One project which is being implemented with resettled small-scale dairy farmers combines biogas plants, cassava for fodder, and the introduction of Jatropha curcas (physic nut) hedges for revegetation and the production of oil. The plant belongs to the family of Euphorbiaceae and is related to the castor oil plant (GTZ, 1993). The project area, the Rusitu Small Scale Dairy Reset- tlement Scheme, is on the eastern border of Zimbabwe with Mozambique (see Fig. 1). The small-scale dairy farmers who are allowed to resettle there are screened for experience and ability, and allocated 4 hectares (ha) each on undulating terrain. Of this, 2.5 ha is used for growing fodder, 1 ha for own crops, and 0.5 ha for buildings Fig 1. Agroecological regions of Zimbabwe (ENDA-Zimbabwe, 1992). (ARDA, 1993). Most of the land is allocated to fodder Rusitu is in region 1, see map key for description.

48 Energy for Sustainable Development ! Volume 1 No. 1 ! May 1994